System for producing a single nonrepetitive scanning trace



H. DE RYDER 2,415,870

SYSTEM FOR PRODUCING A SINGLE NON-REPETITIVE SCANNING TRACE Feb. 18, 1947.

Filed May 30, 1942 m m a 5 0 z a a w 5 Mw mwa mm .n r WZ Inwcntor Gttorneg Patented Feb. 18, 1947 SYSTEM FOR PRODUCING A SINGLE NON- REPETITIVE SCANNING TRACE Herbert De Ryder, Bloomfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 30, 1942, Serial No. 445,184

Claims.

This invention relates to electronic triggering systems and more particularly to circuits adapted to be controlled by successive short duration voltage pulses to produce a single non-repeating square wave of predetermined voltage and a duration time substantially equal to the period between the two successive controlling pulses. A circuit of this character is useful in the measurement of persistence of various phosphors used in cathode ray tubes, when it is desirable to excite a single complete scanning pattern consisting of only one beam trace from upper left corner to the lower right corner of the pattern. This can be done by biasing the control grid of the cathode ray tube to cut off the beam, and applying a square wave of voltage in opposition to the bias voltage during one scanning period.

It is an object of this invention to provide a method and means for generating a square wave of predetermined amplitude and of a length determined by the interval between two control pulses. A further object is the provision of means for exciting a single discrete scanning pattern on the face of a cathode ray tube. Another object is to provide means for controlling the grid of a cathode ray tube by a single square wave pulse derived from the voltage used to control a deflection voltage generator connected to said tube.

These and other and incidental objects will become apparent to those skilled in the art upon consideration of the following description of the invention, with reference to the accompanying drawing, which is a schematic diagram of a trigger circuit according to the invention. A block diagram of a circuit for generating scanning voltages is shown, comprising a pulse generator I connected to control a sawtooth generator 3 for horizontal scanning at a relatively high frequency, for example, 12,000 cycles per second. The sawtooth generator 3 is connected to the horizontal deflection circuit (not shown) of a cathode ray tube. The output of the pulse generator is also connected to a frequency divider I which produces voltage pulses 9 similar in shape to the pulses generated by the generator I, but at a much lower frequency, for example, 60 cycles. The pulses 9 control a sawtooth generator which is connected to the vertical defiection circuit of the cathode ray tube 5. The system thus far described will produce on the screen of the cathode ray tube 5 a scanning pattern of substantially rectangular outline comprising 200 parallel horizontal lines, repeated 60 times per second. The beam describes a zig zag path down the area of the pattern, travelling 'much faster from right to left, during the retrace periods, than it does from left to right. In order to produce a single trace of the pattern, it is necessary to turn the beam on at the beginning of a scanning cycle and cut it ofi at the end of that cycle. A circuit for this purpose is illustrated, comprising two gas filled grid controlled discharge tubes l3 and I5, with their plate circuits connected in series across a direct current source I! when switches are closed. A load resistor I9 is connected across the tube l5. Thus when the tube I3 is conductive and the tube |5 is cut off, current will flow fromf'the source I! through the tube l3 to the resistor l9, producing a voltage drop across the resistor. When both tubes are conducting, the resistor I9 is effectively short circuited by the tube I5, and current from the source flows through the two tubes I3 and l5 but does not cause a substantial voltage across the resistor l9. A resistor 2| is provided in the plate circuit of the tube I3 to limit the current drawn from the source I! when both tubes are conductive. Thus it is possible to produce a voltage pulse of square wave form across the resistor H! by causing the tube I5 to conduct for ending the pulse. The operation cannot be repeated until the plate circuit of the tubes is broken, allowing the grids to regain control of the plate current. Control voltages for the grids of the tubes l3 and I5 are derived from the synchronizing pulse 9 by means of a pulse differentiatin circuit, disclosed and claimed in copending application Serial No. 448,210, filed by O. H. Schade on June 24, 1942. A single stage amplifier 23 inverts the wave 9 to the form 25; the wave 25 is applied to a differentiating circuit comprising a capacitor 2'! and a resistor 29, producing a Wave 3| across the resistor 29. A steady bias potential taken from a voltage divider 33 across a source 35 is added to the wave 3|. and the sum of the two voltages is applied to the grid of the tube l3. The voltage divider 33- is adjusted so that the first positive peak in the wave 3|, occurring at a time Tl, will overcome the bias and fire the tube |3, which will continue to conduct thereafter regardless of the voltage applied to its grid until the plate circuit is broken. Control voltage for the tube I5 is also derived from the synchronizing pulse 9, which is differentiated in a circuit comprising a capacitor 3i and a resistor 39 to produce a wave 4|. A steady bias derived from a voltage divider 43 across the source 35 is added to the wave 4|, and adjusted so that the first positive peak of the wave 4| occurring after the plate voltage is applied to the tube I5 through the tube l3 will fire the tube |5. This happens at the time T2. Thus a voltage 45 is produced across the resistor l9, starting at the beginning of a scanning cycle as determined by the timing wave 9, and ending at the end of the same scanning cycle, without repetition. In order to reset the circuit, switches 41 and 49 are provided in the plate cirintervals, one of the switches, for example, the, switch 41, may be opened and closed periodi-* cally by a clockwork mechanism,'not shown, while the switch 49 remains closed.

Thus the invention has been describedas means 7 for producing a single square'wave ,voltagepulse during the interval between two successive pulses of a repeating voltage wave. This is accomplished by using the first control pulse to connect a voltage source to a utilizationpircuit through a grid controlled gaseous discharge tube, and using the second pulse to short circuit the utilization 'circuit through a'seoond gaseous discharge tube. Since the grid of a tube of this type'loses control over the'plate current after its flow is initiated, the square wave pulse is not repeated until the circuit is reset by breaking theplate circuits.

I claim as my invention:

,1. A system for producing a, single-nonrepetitive, scanning trace on the face of a cathode ray tube, including a source of control impulses, a sawtooth wave generator controlled by said control impulses and connected to one deflecting circuit of a cathode ray tube, a frequency divider arranged to derive a voltage subharmonically related in frequency to said control pulses, a second sawtooth wave generator controlled by the output of said frequency divider and connected to a-second deflecting circuit of said cathode ray tube, means forv applying a bias to a beam control electrode of said cathode ray tubeso as to out off the electron beam of said tubermeans for overcoming said bias during the period between two successive maxima of the output voltage of said second sawtooth wave generator comprising a source of direct current, a resistor coupled to the circuit of said beam control electrode and connected to said direct current source through a gaseous discharge tube, a second gaseous discharge tube connected to shunt said resistor, and means responsive to two successive pulses in the output of said frequency divider to fire respec tively said first and secondgaseous discharge tubes, whereby the electron beam of said cathode ray tube is enabled to reach the fluorescent screen of said tube during the period of a single com:

plete scanning cycle. 7

2. A system for producing a single non-repetitive scanning trace on the face of a. cathode ray tube, including deflection voltage generators connected to the deflection circuits of a cathode ray tube, means arrangedto supply abias toa beam control electrode of said tube whereby the electron beam of'said tube is cut off, and means for overcoming said bias during the period between .tWO successive maxima of the voltage produced by one of said deflection voltage generators including a source of directcurrent, a resistor coupled to said beam control electrodeand connected to said direct current source through a voltage responsive switching device, a second voltage responsive switching device connected to shunt said resistor, and means for deriving voltages related to the output of one of said deflection voltage generators to operate said switching devices successively.

. 3. A system for producing a non-repetitive voltage pulse of predetermined amplitude and 4 duration including a s urce of cyclically repeating control impulses, a voltage responsive switching device having a control input circuit, a. source of direct current, a load connected to said direct current source through said voltage responsive switching device, 1 a second voltage responsive switching device connected in parallel with said load and. having a control input circuit, diiferentiating circuits connected between said source of control impulses and said control input circuits of said voltage responsive switching devices, and means for applying said control impulses to said, differentiating circuits in opposite polarities whereby said first voltage responsive switching device is actuated upon the occurrence of one of said control impulses to connect said direct current source to said load, and said second voltage responsive device is actuated upon the oc currence of the next following control impulse to short circuit said load.

4. The invention set forth in claim 3 wherein said voltage responsive devices comprise electron discharge tubes.

5. A system for producing a single non-repetitive scanning'trace on the face of a cathode ray tube provided with deflection control circuits and an intensity control electrode, including a. source of control impulses, deflection voltage generators controlled by said impulses and connected to said deflection control circuits, means for supplying a bias to said intensity control electrode whereby the electron beam of said tube is cut on, and means for overcoming said bias during the period between two successive maxima of the voltage produced by one of said deflection voltage generators including a source of direct current, a resistor coupled to said intensity control electrode and connected to said direct current source through a voltage responsive switching device, a second voltage responsive switching device connected in parallel with said resistor, differentiating circuits connected between said source of control impulses and said voltage responsive switching devices, and means for applying said control impulses to said differentiating circuits in opposite polaritieswhereby said first voltage responsive switching device is actuated upon the occurrence of one of said controlimpulses to connect said direct current sourceto said resistor, and said second voltage responsive device is actuated upon the occurrence of the next following control impulse to short circuit said resistor. V

' HERBERT DE RYDER.

REFERENCES CITED The following references are of record in the file of this patent: Y 1

UNITED STATES PATENTS: V

Date 1 OTHER REFERENCES Electronics, January 1942, Photoflash Synchronizer Tes'tenby P. A. Marsal, pp. 34 and35. 

